Liver and biliary system pathology in equine dysautonomia (grass sickness).

Hepatocellular and hepatobiliary damage was assessed in equine acute, subacute and chronic grass sickness cases (AGS, SAGS, CGS). Histopathological analysis showed that even in some early AGS cases enlarged hepatocytes, hepatocyte vacuolation indicative of lipid accumulation (steatosis), intrahepatocyte, canalicular and periportal deposition of pigments, frequent leucocyte infiltration and cholangitis occurred. Analysis of serum indicated significantly increased levels of unconjugated bilirubin in all groups and conjugated bilirubin in AGS and SAGS groups, increased levels of bile acids in some individuals from each group and significantly increased levels of glutamate dehydrogenase (GLDH) in AGS and SAGS cases. Conjugated bilirubin was significantly elevated in urine of AGS and SAGS cases. The evidence suggests that abnormal liver function involving moderate hepatocellular pathology in conjunction with steatosis and cholestasis may contribute to the pathogenesis of GS.

The combined effect of cyclosporine a and gentamicin on enzymuria in the Sprague-Dawley rat.

Male Sprague-Dawley rats (8 per group) were administered a single oral dose of cyclosporine A (10, 30 and 50 mg/day) for 5 days or vehicle (corn oil, 1.5 mL/kg) and urinary enzymes excretion was monitored. Only minor changes in enzymuria were observed in the 10 and 30 mg/kg group. However, in the 50 mg/kg group, nephrotoxicity was evident by significant increase in the excretion of N-acetyl-beta-D-glucosaminidase (NAG), glutamate dehydrogenase (GDH), and lactate dehydrogenase (LDH on day 2 of treatment. As chemotherapeutic drug interaction with cyclosporine A (CyA) is thought to aggravate its nephrotoxicity, the effect of combined CyA (30 mg/kg) and the antibiotic gentamicin (50 mg/kg) for 5 days was investigated. Gentamicin alone caused a significant enzymuria, whilst co-treatment of rats with CyA gave rise to increased changes in enzymuria on days 1 and 2, between the groups receiving gentamicin+vehicle and those receiving CyA+gentamicin. This was particularly marked by significant changes in LDH excretion. In contrast these observed differences were not paralleled by changes in serum creatinine and other functional parameters. Treatment with gentamicin, appears to enhance CyA nephrotoxicity, but only in the first 2 days, after this there was no significant differences between the two groups. Our data suggest that urinary enzyme measurements could serve as a valuable non-invasive means of monitoring renal performance in animals or humans who may be exposed to combination of drugs. CyA is found not to potentiate the nephrotoxic effect of gentamicin in the animal model used in this study. It therefore appears safe to use the combined therapy particularly in the treatment of transplant patients.

Time course of chronic oral cadmium nephrotoxicity in Wistar rats: excretion of urinary enzymes.

Twelve male and female Wistar rats each received cadmium (as CdCl2) in their diet at concentrations of 0, 10, 50, and 250 ppm for 72 weeks. After 1, 4, 8, 13, 18, 26, 32, 45, 57, and 68 weeks a total of 8 enzymes from different cellular compartments of the nephron were measured. At the end of the study period, the kidneys were examined histopathologically. Concentrations up to and including 50 ppm did not induce any adverse effect. At 250 ppm, growth of male and female animals was markedly retarded. Significantly increased activities of the cytosolic phosphohexose isomerase were excreted by males and females receiving 250 ppm at all timepoints from week 13. The values of the mitochondrial glutamate dehydrogenase were mostly elevated from week 1 to 57, however, due to a wide scatter range, were only occasionally significantly different from control values. The brush border enzymes (gamma-glutamyl transferase, alkaline phosphatase and leucine arylamidase) were not changed in a relevant manner in female rats, while in 250 ppm males the excreted activity of ALP and LAP from week 1 to week 18, and that of GGT during the entire study period were significantly lower than the control values. Excretion of the lysosomal enzymes aryl sulfatase A, beta-galactosidase, and beta-N-acetyl-D-glucosaminidase was at no time influenced in a noteworthy manner. Histopathology after 72 weeks revealed chronic but also acute degenerative changes in the kidneys of 250 ppm males and females. A comparison of published data on persons having undergone high cadmium exposure with the results presented here shows remarkable differences.

Renal damage caused by gentamicin: a study of the effect in vitro using isolated rat proximal tubular fragments.

The clinical use of gentamicin (G) is limited because of its nephrotoxic potential. The administration of G (50 mg/kg) to rats in a 10-day daily treatment gave a biphasic pattern of lactate dehydrogenase (LDH) and N-acetyl-beta-D-glucosaminidase (NAG) excretion. Alkaline phosphatase (ALP) was highly elevated during the corresponding second phase while a slight and statistically insignificant increase in glutamate dehydrogenase (GDH) was obtained. The kidneys of such rats were isolated and tubules prepared and incubated for a specific period of time at 37 degrees C in Kreb's Henseleit bicarbonate buffer, pH 7.4. Results indicate a considerable loss of protein (P < 0.01) after the 3rd and 10th days of treatment with G, elevated and significant increase of ALP after the 1st (P < 0.05) and 3rd (P < 0.01) days and significant increase (P < 0.05) of GDH after the 10th day of treatment. The release of GDH, LDH and NAG from tubules of rats after a single dose of G was lower than the control rats while other treatments produced a significant increase in ALP, LDH and NAG over the period of incubation. In vitro incubation of tubules in the presence of several concentrations (5, 50, 500, 5000 micrograms/g of wet cortex) of G indicated a time-dependent leakage of enzyme only at the highest concentration of G. Our results clearly indicate that cellular damage caused by G as evidenced by urinary enzyme excretion and marker enzyme release from isolated tubules occurs at very high concentration in vivo or in vitro and is time-dependent.

In vivo nephrotoxic action of an isomeric mixture of S-(1-phenyl-2-hydroxyethyl)glutathione and S-(2-phenyl-2-hydroxyethyl)glutathione in Fischer-344 rats.

An isomeric mixture of S-[(1 and 2)-phenyl-2-hydroxyethyl]glutathione (PHEG), a glutathione conjugate of styrene, is moderately nephrotoxic. Its in vivo nephrotoxicity was characterized by significant elevations in the urinary excretion of glucose, gamma-glutamyl transpeptidase, glutamate dehydrogenase, N-acetyl-beta-D-glucosaminidase and lactic dehydrogenase 24 h after an i.v. administration of PHEG (0.5 mmol/kg) in male Fischer-344 rats. The histologic alterations consisted of moderate tubular damage with proximal tubule vacuolization and accumulation of tubular cast material, indicating an early sign of tubular necrosis. The data suggest that nephrotoxic injury induced by PHEG lies preferentially at the tubular region of the rat kidney involving several subcellular targets. The nephrotoxicity of PHEG was blocked by acivicin, a specific inhibitor of gamma-glutamyl transpeptidase, by phenylalanylglycine, an inhibitor of cysteinylglycine dipeptidase, as well as by probenecid, a competitive inhibitor of renal organic anion transport system. On the other hand, pretreatment with aminooxyacetic acid, a specific inhibitor of renal cysteine conjugate beta-lyase, failed to inhibit the nephrotoxicity of this glutathione conjugate. Similarly, prior administration of alpha-ketobutyrate, an inducer of renal cysteine conjugate beta-lyase, failed to potentiate its nephrotoxicity, suggesting an insignificant role of beta-lyase in such toxicity. A modest decline in renal cellular GSH due to PHEG but without any concomitant oxidation of GSH to GSSG and without any increase in lipid peroxidation indicates that oxidative stress may not be an important mechanism of its nephrotoxicity. Therefore, the following steps at least, are involved in the development of its nephrotoxicity: (1) renal tubular accumulation of PHEG via a probenecid-sensitive transport process; and (2) its renal metabolism via gamma-glutamyl transpeptidase and cysteinylglycine dipeptidase to the corresponding cysteine-S-conjugate.

Ammonium metabolism: emphasis on energy considerations.

The metabolism of a typical North American diet yields a net acid load. Hydrogen ions are removed from the body after combining with bicarbonate to form CO2. This leaves the body with a deficit of bicarbonate. The role of the kidney is to add 'new' bicarbonate to the body. It does so primarily by synthesizing NH4+ plus bicarbonate while making NH4+ an end-product of metabolism (excreting it in the urine). Production of NH4+ occurs primarily in proximal convoluted tubule cells. Although several possible pathways can do this, the primary one stimulated by chronic metabolic acidosis is the glutaminase/glutamate dehydrogenase one. The upper limit on this pathway is set by energy turnover considerations. This, in effect, means control by renal work (sodium reabsorption) and fuel competitions (availability of fat-derived fuels).

The nephrotoxic potential of gentamicin in the cat: enzymuria and alterations in urine concentrating capability.

This study investigated the potential for nephrotoxicity of gentamicin in cats by measuring marker enzyme concentrations, [Na], [K], osmolality, and pH of the urine, and blood urea nitrogen (BUN) levels. Gentamicin was administered i.m. at 4.4 mg/kg once daily (s.i.d.) or twice daily (b.i.d.) for 7 days. Concentrations of lactic dehydrogenase (LDH), lysozyme (LZM), alkaline phosphatase (AP), and glutamate dehydrogenase (GD) were measured as total 24-h excretions. The s.i.d. regimen produced only a slight increase in LDH excretion after 5 days, whereas the b.i.d. regimen caused an increase in the excretion of all enzymes. The greatest elevations were observed for LZM and LDH. Of the enzymes studied, these appeared to be the most appropriate to monitor for potential nephrotoxicity, except that urinary concentrations did not correlate well with duration of gentamicin administration. Only slight elevations in BUN were observed for either regimen. Single daily administration increased urine osmolality slightly, but b.i.d. treatment caused a marked and immediate decrease in urine osmolality, [Na], and total Na excretion. Urinary [K] was also depressed, as was total K excretion after 6 days. Urine pH was not substantially affected. This study showed that the recommended daily dose of 4.4 mg/kg produced little if any evidence of nephrotoxicity as indicated by the parameters measured. Twice daily dosing, however, produced elevations in urine enzyme concentrations, and markedly decreased urine osmolality and Na and K excretion. Compared to other species studied, the cat appears particularly sensitive to urine concentrating alterations resulting from repeated gentamicin administration.

Assessment of renal injury by urinary enzymes.

The use of serum enzymes in the detection of tissue damage due to disease or toxins is now well established but the full potential for the use of urinary enzymes to detect and monitor kidney damage has not been realized. There are a number of problems involved in dealing with urinary enzymes and these have not always been fully appreciated by research workers. This report discusses some of the difficulties and how they can be overcome.

Biochemical changes in the rat during experimentally induced acute ochratoxicosis.

Biochemical changes in rat urine and tissues treated with five consecutive daily doses of ochratoxin A (10 mg/kg body weight) were studied. Urine volume and urinary proteins were moderately raised during the first few days of ochratoxin treatment, and were then highly elevated towards the end of the investigation. Urinary muramidase excretion was significantly raised (p less than 0.01) 24 h after the first insult with the toxin. The urinary output of alkaline and acid phosphatases, lactate dehydrogenase (LDH) and glutamate dehydrogenase (GDH) were all elevated but very much later, during the course of injections with ochratoxin A. Kidney alkaline and acid phosphatases, LDH and GDH were correspondingly reduced 7 days from the beginning of ochratoxin A administration. Liver LDH activity was reduced while serum LDH was raised. Liver glycogen level was significantly (p less than 0.0001) increased. Experimental evidence was presented to show that the initial point of interaction of ochratoxin A with the rat renal system may be at the first portion of the proximal convoluted tubular cell region.

Protection by selenium against gentamicin-induced acute renal damage in the rat.

Gentamicin has been shown to induce renal tubular damage in man and laboratory animals and to result in elevated urinary excretion of some enzymes associated with specific cell regions in the kidney. In the present investigation, the possible protective effect of selenium against gentamicin-induced renal damage was tested by measuring the urinary excretion of some enzymes in the presence and absence of selenium. Our results show that a prior subcutaneous injection of selenium to rats for two days followed by a simultaneous S.C. injection of gentamicin and selenium resulted in a marked reduction in the excretion of such biochemical systems as the urine volume, urinary proteins, alkaline and acid phosphatases, beta-glucuronidase, muramidase, and glutamate dehydrogenase. Renal functional studies revealed that selenium-treated rats suffered less adverse effects compared to rats treated with gentamicin alone. Urinary acid phosphatase, beta-glucuronidase and muramidase, the three lysosomal enzymes tested, appeared to respond most readily to protection by selenium.

Renal effects of an aminoglycoside antibiotic in the rat.

The renal effect of the daily administration of gentamicin to male albino rats (20 mg/kg body weight) for 6 consecutive days on some biochemical systems of the kidney was examined. Urine volume and urinary protein levels were found to be progressively raised following gentamicin. Urinary alkaline phosphatase, acid phosphatase, muramidase and glutamate dehydrogenase (GDH) activities were found to be markedly elevated. Acid phosphatase and GDH activities in urine were raised 24 h and 48 h, respectively, from the onset of gentamicin administration. The sequence in which some regions of the renal cells were involved in gentamicin nephrotoxicity was determined and the probable mechanism of interaction of gentamicin antibiotic with the renal tubular cells is proposed.

Urinary enzyme excretion and renal lactate dehydrogenase isoenzyme pattern in acute HgCl2 nephropathy of rat.

The activity of several enzymes with different intracellular sites was determined in urine at various times following nonfatal acute tubular necrosis induced by mercuric chloride administration. The excretion rate of all tested enzymes rose on the 1st and 2nd day; in the next observations (days 7-15) enzymatic values approached the basal values. The lactate dehydrogenase isoenzyme pattern of the renal cortical zone showed an early shift towards cathodic fractions and later (7 days) an increase of middle ones; the normal anodic zymogram recovered after a suitable time interval (30 days). The isoenzymatic changes are related both to the renal hypoxia and to the appearance of less differentiated cells. The behaviour of functional parameters (urine flow, osmolality, urea clearance, creatinine clearance) were well in agreement with the observed enzyme and renal isoenzyme changes.

The sensitivity of urinary enzyme measurements for detecting renal injury.

The relative sensitivity of urinary enzyme measurements for detecting renal damage was determined for two nephrotoxins. Injection of a single dose of sodium phosphate (10 mmoles/kg) caused damage to the proximal tubules and led to a 15 fold increase in lactate dehydrogenase (LDH) activity excreted into the urine. In contrast to this change the serum LDH remained normal. Similar results were obtained following the injection of cephaloridine (2 g/kg) with an 18 fold increase in urinary LDH and a marginal increase in urinary glutamate dehydrogenase (GDH). By contrast the serum LDH was unchanged. Urinary enzymes are therefore more sensitive for detecting renal injury than enzymes. The four enzymes investigated are located in specific regions of the cell so that the involvement of the organelles and regions of the cell can be followed. Damage to the organelles does not appear to occur as the excretion of the lysosomal enzymes remained normal and only in the case of cephaloridine were marginal changes in the mitochondrial GDH excretion seen. The average alkaline phosphatase was also normal suggesting no gross damage to the plasma membrane although a few individual rats excreted abnormal activities of alkaline phosphatase. These rats however, also excreted high activities of LDH. This suggests that damage to the membrane causes leakage of LDH and in severe cases release of the plasma membrane enzyme alkaline phosphatase. The administration of cephaloridine at various doses showed that urinary enzyme measurements were as sensitive as histology for demonstrating renal damage and that of these enzymes, LDH was by far the most useful.

Urinary enzymes and kidney damage by aspirin and phenacetin.

Two groups of rats were given aspirin and phenacetin in their food at daily doses similar to those taken by humans suffering from analgesic abuse. Both drugs damaged the kidney proximal tubules although phenacetin affected the kidney more severely than aspirin. At the start of the experiment aspirin increased the urinary excretion of lactate dehydrogenase (LDH) while phenacetin raised the excretion of all four enzymes studies (acid phosphatase, alkaline phosphatase, glutamate dehydrogenase (GDH), LDH indicating generalised cellular injury. Subsequent samples of urine collected from rats up to seven weeks showed normal urinary enzyme levels. The value of urinary enzyme measurements in detecting renal damage by drugs is discussed.